RE: DNS behaviour with MX preferences...
Most SMTP servers will try all listed MX records (in increasing preference order) prior to queuing for later delivery. Your assumption is correct that mailgate1 would receive all inbound traffic (to its connection limits). -- Roger D. Seielstad - MCSE Sr. Systems Administrator Peregrine Systems Atlanta, GA > -Original Message- > From: Adam Romain [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, April 23, 2002 5:50 AM > To: Exchange Discussions > Subject: DNS behaviour with MX preferences... > > > Guys, > > I'm trying to fully understand what happens with MX > preferences and SMTP relays. > > Let me draw a picture. Lets says a company has 2 SMTP > inbound connections for domain name example.com and the MX > records show that example.com has 4 servers that will accept > the mail. i.e. mailgate1.example.com pref = 10, > mailgate2.example.com with pref = 20, fallback1.isp.com pref > = 50 and fallback2.isp.com pref = 50. > > If mailgate1 is always available, will it be the only > connector that takes the mail unless it has reached the > maximum number of sessions ? > > If mailgate1 is down, how quickly does the sending SMTP > connector give up and try the next MX record pref, i.e > immediately or after a certain retry parameter ? > > TIA > > Adam Romain > ** > This email and any files transmitted with it are confidential > and intended solely for the use of the individual or entity > to whom they are addressed. If you have received this email > in error please notify the system manager. > > Network Defence Ltd > ** > > _ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Archives: http://www.swynk.com/sitesearch/search.asp > To unsubscribe: mailto:[EMAIL PROTECTED] > Exchange List admin:[EMAIL PROTECTED] > _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
RE: DNS behaviour with MX preferences...
Cheers Bud. -Original Message- From: Benjamin Scott [mailto:[EMAIL PROTECTED]] Sent: 23 April 2002 13:05 To: Exchange Discussions Subject: Re: DNS behaviour with MX preferences... On Tue, 23 Apr 2002, at 10:50am, Adam Romain wrote: > If mailgate1 is always available, will it be the only connector that > takes the mail unless it has reached the maximum number of sessions ? In theory, yes. In practice, "always available" is not a realistic condition. Some random mail exchanger on the Internet may have trouble contacting mailgate1 for some reason unrelated to your systems, and end up using mailgate2 instead. > If mailgate1 is down, how quickly does the sending SMTP connector give > up and try the next MX record pref, i.e immediately or after a certain > retry parameter ? This is implementation-specific. Most of the SMTP implementations I have seen try the next MX immediately. -- Ben Scott <[EMAIL PROTECTED]> | The opinions expressed in this message are those of the author and do | not | necessarily represent the views or policy of any other person, | entity or | organization. All information is provided without | warranty of any kind. | _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED] ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Network Defence Ltd ** _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
RE: DNS behaviour with MX preferences...
Alternatively, you can put multiple servers behind a local director device and advertise the virtual name/IP as your smtp host with the lowest cost. S. -Original Message- From: Matt Monteleone-Haught [mailto:[EMAIL PROTECTED]] Sent: Tuesday, April 23, 2002 6:18 AM To: Exchange Discussions Subject: Re: DNS behaviour with MX preferences... If you'd like them load balanced then have the preferencs set the same. _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
Re: DNS behaviour with MX preferences...
On Tue, 23 Apr 2002, at 10:50am, Adam Romain wrote: > If mailgate1 is always available, will it be the only connector that takes > the mail unless it has reached the maximum number of sessions ? In theory, yes. In practice, "always available" is not a realistic condition. Some random mail exchanger on the Internet may have trouble contacting mailgate1 for some reason unrelated to your systems, and end up using mailgate2 instead. > If mailgate1 is down, how quickly does the sending SMTP connector give up > and try the next MX record pref, i.e immediately or after a certain retry > parameter ? This is implementation-specific. Most of the SMTP implementations I have seen try the next MX immediately. -- Ben Scott <[EMAIL PROTECTED]> | The opinions expressed in this message are those of the author and do not | | necessarily represent the views or policy of any other person, entity or | | organization. All information is provided without warranty of any kind. | _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
RE: DNS behaviour with MX preferences...
Cheers, that's cleared that up! Adam -Original Message- From: Matt Monteleone-Haught [mailto:[EMAIL PROTECTED]] Sent: 23 April 2002 11:18 To: Exchange Discussions Subject: Re: DNS behaviour with MX preferences... "If mailgate1 is always available, will it be the only connector that takes the mail unless it has reached the maximum number of sessions ?" Yes, although I have seen my 'secondary inbound' box accepting mail when the 'primary' box was clearly available. If you'd like them load balanced then have the preferencs set the same. "If mailgate1 is down, how quickly does the sending SMTP connector give up and try the next MX record pref, i.e immediately or after a certain retry parameter ?" Immediately as far as I understand it. If mail.wheaton.com is unavailable, it then tries mail1.wheaton.com, if that is unavailable, my ISP starts to queue the mail for me and will for the next 24 hours or until one of the MX records with a lower cost becomes available. I believe all of this is outlined in the RFCs. >From RFC 974: "If the list of MX RRs is not empty, the mailer should try to deliver the message to the MXs in order (lowest preference value tried first). The mailer is required to attempt delivery to the lowest valued MX. Implementors are encouraged to write mailers so that they try the MXs in order until one of the MXs accepts the message, or all the MXs have been tried. A somewhat less demanding system, in which a fixed number of MXs is tried, is also reasonable. Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried. In addition, in the special case in which there are several MXs with the lowest preference value, all of them should be tried before a message is deemed undeliverable." Try. http://www.faqs.org/rfcs/rfc974.html Matt - Original Message - From: "Adam Romain" <[EMAIL PROTECTED]> To: "Exchange Discussions" <[EMAIL PROTECTED]> Sent: Tuesday, April 23, 2002 5:50 AM Subject: DNS behaviour with MX preferences... Guys, I'm trying to fully understand what happens with MX preferences and SMTP relays. Let me draw a picture. Lets says a company has 2 SMTP inbound connections for domain name example.com and the MX records show that example.com has 4 servers that will accept the mail. i.e. mailgate1.example.com pref = 10, mailgate2.example.com with pref = 20, fallback1.isp.com pref = 50 and fallback2.isp.com pref = 50. If mailgate1 is always available, will it be the only connector that takes the mail unless it has reached the maximum number of sessions ? If mailgate1 is down, how quickly does the sending SMTP connector give up and try the next MX record pref, i.e immediately or after a certain retry parameter ? TIA Adam Romain ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Network Defence Ltd ** _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED] _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED] ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Network Defence Ltd ** _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
Re: DNS behaviour with MX preferences...
"If mailgate1 is always available, will it be the only connector that takes the mail unless it has reached the maximum number of sessions ?" Yes, although I have seen my 'secondary inbound' box accepting mail when the 'primary' box was clearly available. If you'd like them load balanced then have the preferencs set the same. "If mailgate1 is down, how quickly does the sending SMTP connector give up and try the next MX record pref, i.e immediately or after a certain retry parameter ?" Immediately as far as I understand it. If mail.wheaton.com is unavailable, it then tries mail1.wheaton.com, if that is unavailable, my ISP starts to queue the mail for me and will for the next 24 hours or until one of the MX records with a lower cost becomes available. I believe all of this is outlined in the RFCs. >From RFC 974: "If the list of MX RRs is not empty, the mailer should try to deliver the message to the MXs in order (lowest preference value tried first). The mailer is required to attempt delivery to the lowest valued MX. Implementors are encouraged to write mailers so that they try the MXs in order until one of the MXs accepts the message, or all the MXs have been tried. A somewhat less demanding system, in which a fixed number of MXs is tried, is also reasonable. Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried. In addition, in the special case in which there are several MXs with the lowest preference value, all of them should be tried before a message is deemed undeliverable." Try. http://www.faqs.org/rfcs/rfc974.html Matt - Original Message - From: "Adam Romain" <[EMAIL PROTECTED]> To: "Exchange Discussions" <[EMAIL PROTECTED]> Sent: Tuesday, April 23, 2002 5:50 AM Subject: DNS behaviour with MX preferences... Guys, I'm trying to fully understand what happens with MX preferences and SMTP relays. Let me draw a picture. Lets says a company has 2 SMTP inbound connections for domain name example.com and the MX records show that example.com has 4 servers that will accept the mail. i.e. mailgate1.example.com pref = 10, mailgate2.example.com with pref = 20, fallback1.isp.com pref = 50 and fallback2.isp.com pref = 50. If mailgate1 is always available, will it be the only connector that takes the mail unless it has reached the maximum number of sessions ? If mailgate1 is down, how quickly does the sending SMTP connector give up and try the next MX record pref, i.e immediately or after a certain retry parameter ? TIA Adam Romain ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Network Defence Ltd ** _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED] _ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin:[EMAIL PROTECTED]
